The present invention relates generally to thermal printing systems, and in particular to a single pass multicolor thermal transfer printer.
In thermal transfer printing, an ink or other record-forming material is selectively transferred from a carrier to a record medium, which may be ordinary paper, by applying thermal energy to localized areas of the carrier. Information frequently is printed on the record medium as an arrangement of colored dots or other discrete elements. For example, U.S. Pat. No. 3,453,648 to Stegenga describes a system that includes a number of printing modules, each with thriteen strip-like heating elements. Line segments defining any desired alphanumeric character can be transferred to a record medium from an adjacent ink-coated carrier sheet by energizing the appropriate heating elements in a module. The different modules are mounted in a fixed printing head, one at each potential character position in a line.
The thermal printing unit disclosed in U.S. Pat. No. 3,596,055 to Elston includes a printhead having a 5.times.5 matrix of dot-like semiconductor mesas on one face. The mesas can be selectively heated to an elevated temperature by logic circuitry in the unit to produce a character-defining pattern of hot spots on the printhead face. In use, a motor-driven carriage steps the printhead along a pigmented carrier ribbon supported between the printhead face and a record medium. Certain mesas are energized by the logic circuitry at each successive carriage position, causing spots of pigment forming dot matrix characters to transfer from the carrier ribbon to the record medium. A third type of thermal transfer printer, typified by U.S. Pat. No. 3,984,809 to Dertouzos et al., included a fixed printhead having a single row of thermal elements. The row extends across contigously moving webs of carrier and record media, perpendicular to their direction of travel. By selectively energizing the elements as the webs move past, closely spaced rows of dots are imprinted on the record medium to produce alphanumeric characters or other information in two-dimensional dot patterns.
Two approaches have been used to produce multicolor images by thermal transfer printing. One is a multiple pass method in which a record medium is printed several times with the same printhead using a different color transfer carrier each time. Another is the approach shown in the above-mentioned Dertouzos et al. patent--the record medium is moved in succession past three printheads, each associated with a different color transfer carrier.